Bright green sources of high-energy X-ray light captured by NASA's NuSTAR mission are overlaid on an optical-light image of the Whirlpool galaxy (the spiral in the center of the image) and its companion galaxy, M51b (the bright greenish-white spot above the Whirlpool), taken by the Sloan Digital Sky Survey. The bright green spots at the center of the Whirlpool and M51b are created by material surrounding supermassive black holes; additional X-ray sources in the vicinity contribute to the emission. The known ultraluminous neutron star is located on the left side of the Whirlpool.

NuSTAR is a Small Explorer mission led by Caltech in Pasadena and managed by NASA's Jet Propulsion Laboratory, also in Pasadena, for NASA's Science Mission Directorate in Washington.